egg toothA hard, toothlike projection from the beak of embryonic birds, or from the upper jaw of embryonic reptiles, that is used to cut the egg membrane and shell upon hatching and that later falls off.

tooth or toothlike structure used by the young of many egg-laying species to break the shell of the egg and so escape from it at hatching. Some lizards and snakes develop a true tooth that projects outside the row of other teeth, helps the young to hatch, and then is shed. Turtles, crocodilians, and birds have an analogous horny structure that performs a similar function. The only mammal to hatch from an egg, the duck-billed platypus, also develops an egg tooth before birth.